The introduction of highly active antiretroviral therapy (HAART) for HIV/AIDS has improved survival. However, the prevalence of depression has not significantly changed. Depression is associated with poor clinical outcomes. A higher concentration of anti-HIV medication in the central nervous system (CNS) is hypothesized to be the primary modulator of beneficial neurological response. Several studies in medically related depressive disorders have suggested a role for inflammatory cytokines as provocateurs of depression. The recently described concept of CNS penetration effectiveness (CPE) scores of antiretroviral therapy (ART) allows improved estimation of concentration of antiretroviral (ARV) medication in the CNS whilst eliminating the challenge of obtaining CSF drug concentrations on each patient. Utilizing data from the CNS HIV Antiretroviral Therapy Effects Research (CHARTER) cohort study, we propose to investigate if better CPE of ART reduces depression thereby resulting in better HIV clinical outcomes. We will assess the effect of CPE on adherence to ARV medication. We hypothesize that better CPE will be associated with improved mood and adherence. We also propose to evaluate changes in the inflammatory and trophic environment of the CNS and peripheral blood produced by the CPE of ART. We will assess the association between CPE of ART regimens and levels of CSF/blood pro-inflammatory cytokine mediators of depression, independent of viral load suppression. We hypothesize that increased CPE will decrease CSF and blood cytokines (Tumor Necrosis Factor-alpha, Interleukins-1, 6, and 12 and monocyte chemo attractant protein-1), thereby improving depression. We also seek to elucidate the association between depression and CSF virologic failure. This study will improve our understanding of the neuropathogenesis of HIV and the neurobehavioral effects of ARV treatment with respect to their CPE. This will help improve therapeutic choices for patients with HIV/AIDS and thereby improve clinical outcomes. An insight into changes in CSF/blood pro-inflammatory cytokines associated with the CPE of ART may be helpful in developing HIV treatments that have an additional effect of improving mood.